DESCRIPTION: The purpose of this project is to investigate the relationship between depression and chronic pain using a new, clinically relevant experimental pain technique. Previous research has shown a high incidence of depression in patients with chronic pain and a number of investigators have suggested that depression is a significant factor in the etiology or maintenance of chronic pain syndromes. The two fundamental approaches to the investigation of depression and chronic pain employ either self-report measures of pain or experimental pain induction methods. Both of these approaches have yielded interesting information, but two serious criticisms have been raised about the validity of these approaches. When self-report measures of pain are used to investigate correlational relationships with other self-report measures of depression or negative affect, self report bias or method variance may be largely responsible for the obtained relationships among variables. Experimental pain measures offer better stimulus control and less influence of self-report bias, but are criticized because the experimental pain may not be a valid analog of clinical pain. The investigators recently developed a pain assessment protocol that combines the stimulus control of experimental pain procedures with the relevance of clinical pain. The method employs a back extension rehabilitation device which allows for precise control of the stimulus level (weight), timing and duration of stimuli, and stabilization of the subjects to isolate force production to the injured musculature. When used with back injured individuals, this protocol combines the stimulus control of laboratory pain induction methods with clinically relevant pain. A magnitude-matching psychophysical protocol is then employed to derive a psychophysical function for each subject which indicates the subject's ability to discriminate between levels of stimulation and the subject's response bias, or proclivity to label a stimulus as intense (heavy or painful in this protocol). Additional analyses will test the pain perception differences between depressed and non-depressed patients with chronic pain and sex differences in pain perception. The relationship of self report measures of depression to the discriminability and response bias measures of pain will be investigated in a sample of patients with chronic low back pain. Significant relationships between (a) the somatic component of depression and discriminability and (b) between the cognitive/ affective component of depression and response bias would be supportive of recent neurobiological models of pain and depression. On the other hand, a lack of significant relationships between self-report of depression and the psychophysical measures would suggest that self-report bias may be a confound in much previous research.